PROJECT SUMMARY This proposed research will elucidate the molecular basis of neuronal regulation of adult taste stem cells. Taste organs degenerate in the absence of neuronal input, a phenomenon described more than a century ago, but the cellular and molecular mechanisms underlying this are not well defined. We propose to use a combined in vivo and in vitro approach to determine if R-spondin-2 (Rspo2), via interaction of its taste stem cell-expressed receptors Lgr5/Lgr6 and/or Znrf3/Rnf43, is the gustatory-neuron-produced factor that maintains taste bud integrity. In Aim 1, we will determine if Rspo2 is required for taste bud maintenance. Using a loss-of-function approach, conditional ablation of Rspo2 from gustatory neurons that innervate taste tissue will help determine whether gustatory neuron-produced Rspo2 is necessary to maintain taste bud integrity. Conversely, in a gustatory nerve transection model that leads to taste tissue denervation, we will determine if systemically supplied recombinant Rspo2 via adenovirus and purified protein is sufficient for taste cell generation and taste bud regeneration in the absence of gustatory innervation. The loss-of-function and gain-of-function will establish the role of Rspo2 in neuronal regulation of taste tissue maintenance. In Aim 2, we will determine if Rspo2 interacts with its taste stem cell-expressed receptors Lgr5/Lgr6 and/or Znrf3/Rnf43 to regulate taste stem cell activity. We will use genetic approaches, Rspo2 mutants that selectively bind to Lgr5/Lgr6 or Znrf3/Rnf43, taste organoid culture, and gustatory nerve transection to determine how Rspo2 acts. Cancer patients who receive chemotherapy or radiotherapy often experience taste disturbance. The distortion or loss of taste can lead to appetite loss and malnutrition. The mechanisms for drug-induced taste disturbance are not clear, but dysregulation of adult taste stem cell activity could be the culprit. Accomplishing the aims proposed here will be significant steps toward developing strategies for mitigating taste disturbances experienced by individuals who suffer from taste loss or taste distortion.